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2012-03-26_REVISION - M1977493
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2012-03-26_REVISION - M1977493
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Last modified
8/24/2016 4:55:30 PM
Creation date
3/28/2012 2:46:43 PM
Metadata
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Template:
DRMS Permit Index
Permit No
M1977493
IBM Index Class Name
REVISION
Doc Date
3/26/2012
Doc Name
DRMS ADEQUACY REVIEW
From
CLIMAX MOLYBDENUM
To
DRMS
Type & Sequence
TR20
Email Name
ECS
Media Type
D
Archive
No
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SECTIONFIVE Conclusions and Recommendations <br />URS was requested by Climax to perform an independent check of the seepage and stability <br />analyses for 3 Dam to satisfy the DRMS third -party review requirements prior to initiating <br />deposition activities. Seepage analyses were completed for 3 Dam to calibrate the existing <br />phreatic surface and predict future phreatic levels during active deposition. Slope stability <br />analyses for 3 Dam included evaluating steady -state and post - earthquake loading conditions for <br />the existing height and the future design height using current seepage analysis results under the <br />operating conditions. <br />Presented below is a summary of conclusions followed by recommendations for further actions. <br />Conclusions and recommendations were developed based on the results of the analyses and on <br />our experience with these and other tailing dams. <br />5.1 CONCLUSIONS <br />Steady -state seepage and post - earthquake stability analyses were completed for the dam at its <br />existing height for the operating condition. The phreatic surface was based on values calculated <br />using a revised seepage model. Liquefaction analyses completed indicated the material has a <br />low risk for liquefaction under the design earthquake. The stability results for the maximum dam <br />section, presented in Table 4 -3, indicate the dam meets or exceeds the minimum FS design <br />criteria. <br />Steady -state seepage and post - earthquake stability analyses were also completed for the future <br />design height for the design earthquake. The proposed future height is a 13 -foot increase to the <br />raise berm that is stepped back from the existing dam crest. The phreatic surface was based on <br />the current seepage model that showed a slight increase in the phreatic surface due to active <br />deposition. Liquefaction analyses completed indicated the material has a low risk for <br />liquefaction under the design earthquake. The stability results for the maximum dam section, <br />presented in Table 4 -3, indicate the dam meets or exceeds the minimum FS design criteria. <br />Our stability analysis results confirm the dam meets steady -state and post - earthquake stability <br />criteria for both existing height and future design elevations under operating conditions. <br />5.2 RECOMMENDATIONS <br />The operation of 3 Dam will depend on the proper management of the tailing facility and <br />emplacing tailing with properties envisioned for this dam. With a new mill, it will be important <br />to observe and capture the material properties and changes and evaluate potential impacts tailing <br />operations may have on operation of the facility. <br />Comparing deposited mill tailing with those presently emplaced is important to the overall <br />successful operation of the facility and part of what is known as the "observational approach." <br />The observational approach consists of evaluating the in -place tailing properties with those <br />modeled in the original analysis. It is an iterative process that occurs throughout the life of the <br />dam. With this in mind, we recommend the following actions when deposition resumes: <br />> Perform beach profile sampling to evaluate newly deposited tailing to verify the material <br />properties are consistent with those envisioned in the design. This will include evaluating <br />the whole tailing gradation as it compares to past whole tailing gradations. Profile <br />sampling should be performed near the end of the first spigot season (estimated late <br />summer /early fall 2012). The sampling includes collection of relatively undisturbed <br />UM N IPROJECTS122242095 _CLIMAX STARTUP PROJISUB 881120 WORD PROCI3 DAM SEEPAGES TABILRYTINALWINAL _3 DAM ANALYSES RPT R4 DRMS DOCX 5 -1 <br />
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